Vapor generating superheating and reheating unit



J. H. AMMON 3,279,439

VAPOR GENERATING SUPERHEATING AND REHEATING UNIT Oct. 18, 1966 4 Sheets-Sheet 1 Filed June 5, 1964 INVENTOR. Johannes H. Ammon ATTORNEY Oct. 18, 1966 J. H. AMMON 3,279,439

VAPOR GENERATING SUPERHEATING AND REHEATING UNIT Filed June 5, 1964 4 Sheets-Sheet 2 J. H. AMMON Oct. 18, 1966 VAPOR GENERATING SUPERHEATING AND REHEATING UNIT 4 Sheets-Sheet 5 Filed June 5, 1964 J. H. AMMON Oct. 18, 1966 4 SheetsSheet 4 Filed June 5, 1964 United States Patent O 3,279,439 VAPOR GENERATING SUPERHEATING AND REHEATING UNIT Johannes H. Ammon, Akron, Ohio, assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed June 5, 1964, Ser. No. 372,860 17 Claims. (Cl. 122-34) This invention relates to a fluid heated vapor generating unit and, more particularly, to a heat exchanger incorporating vapor generating, superheating and reheating tubular heat exchange surfaces all within a single shell.

One of the difliculties in combining a vapor generator, superheater and reheater into a single unit is in devising a tube arrangement which, while providing the required heat exchange surfaces, will aiford minimum containment vessel diameter and height. Another problem in such a unit is in providing a construction which will facilitate assembly, disassembly and maintenance of the component parts. Additionally such :a unit, particularly one employing liquid metal as the heating medium, must provide adequate structural features to withstand any accidents resulting from the interaction of the heating and heated fluids.

It is a primary object of the present invention to in clude the reheater surfaces with the vapor generator and superheater surfaces within a single vessel without thereby disadvantageously increasing the height or diameter of the vessel.

Another object of the invention is to provide a heat exchanger in which the vapor generator tubes are completely drainable to facilitate properly controlling the chemistry of the vaporiz-able fluid.

Still another object is to construct a unit structurally capable of withstanding any violent reaction resulting from the interaction of the heating and the heated fluids.

Yet another important object of the invention is to provide a heat exchanger construction such that even when utilizing a high temperature heating fluid, the walls of the vessel will not be subjected to the extremes of thermal stresses induced by high temperature differentials.

A further object of the invention is to provide a unit arrangement which will facilitate both assembly and disassembly.

Accordingly, the present invention comprises an integral vapor generating, superheating and reheating unit wherein the heating fluid passes in indirect heat transfer relationship over the tubular surfaces which contain the vaporizable fluid. The arrangement of heating surface comprises a bank of vertically extending vapor generator tubes positioned in the lower end of a pressure vessel with banks of superheater and reheater tubes superjacent thereto. To minimize the height of the pressure vessel, the superheater tubes are arranged in annular array concentrically about and coextensive with the reheater tubes. Positioned between the banks of superheater and reheater tubes is a baflie which provides separate flow paths for the heating fluid passing over each of the banks.

The fluid to be heated passes initially through the generator tube bank which is drainable. To accomplish this, the inlets for supplying fluid to the bank of vapor generator tubes are subjacently located in the lower end of the pressure vessel, while the vapor generator tube outlets are located above the bank. Both the inlet and outlet connections for the banks of superheater and reheater tubes are located above the tubes and are also formed integrally with the pressure vessel.

To permit removal of the individual bank of tubes,

the pressure vessel is composed of a number of separately removable, circumferentiallly extending wall sections. The several banks, together with the inlet and outlet chambers are each connected to the appropriate wall section so that they can be removed as individual units. Heating fluid inlet means extend downwardly into the vessel from the upper head and are disposed so that the superheater and reheater tubes each receive separate streams of heating fluid.

Further, individual liner sections within and closely spaced from the pressure vessel wall cooperate to form suitably disposed annular spaces. Inlet and outlet means are arranged in the pressure vessel for fluid supply to and drainage of each of these annular spaces. In addition, an axially extending pipe is arranged within the pressure vessel which, by passing through the several banks of tubes, permits the escape of any gases resulting from the reaction between the heating and heated fluids.

The various objects, features and advantages of the invention will appear more fully from the detailed description which follows, taken in connection with the accompanying drawing.

Of the drawings:

FIG. 1 is a vertical sectional view of a vapor generating, superheating and reheating unit embodying the present invention;

FIG. 2 is a sectional view taken along line 22 in FIG. 1;

FIG. 3 is a sectional view taken along line 33 in FIG. 1;

FIG. 4 is a top view of the unit shown in FIG. 1 with a portion of the heating fluid inlet system within the vessel shown in dashed lines; and

FIG. 5 is an enlarged sectional view taken along line 55 in FIG. 3.

The unit disclosed herein is a further development of the vapor generating and superheating unit set forth in the copending application Serial No. 261,636, dated February 28, 1963, filed in the name-s 0f Johannes H. Ammon and Theodore S. Spr-ague, which application is also owned by the assignee of this application.

In the arrangement shown in FIG. 1 a vapor generating, superheating and reheating unit 10' is disposed Within a vertically extending cylindrically shaped pressure vessel 12. The vessel 12 comprises a lower head 14 contoured for connection to a throat forging 16 which, at its lower end connects to a combined feedwater inlet-sodium outlet member 18. Serially disposed above the lower head are first, second, third, fourth and fifth wall sections 20, 22, 24-, 26- and 28, respectively, topped by upper closure head 30. Wall section 20 is welded about its lower edge to the lower head 14 and has a flanged upper edge. In addition, the vessel is supported by means of the skirt 3'1 integrally attached to and extending downwardly from wall section 20. The remaining wall sections 22, 24, 26 and 28 have flanges about both their lower and upper edges for securing adjacent sections. Additionally, the closure head 30 is flanged for connection to the adjacent wall section 28. These various wall sections and the upper head are bolt-connected together to facilitate disassembly of the vessel and removal of its internals.

Closely spaced from, and in combination with, the interior of the pressure vessel a number of liner sections 32, 34 and 36 form annular flow spaces 38, 40, 42, respectively. As indicated by inlet 44 and outlet 46, connections are provided for delivering a fluid to flow space 3 8 and for draining the fluid and any accumulations from this space. Though not shown, similar connections are provided for the annular flow spaces 40, 42 whereby a gas or other fluid may be introduced into the space between the liner and the shell for limiting the eflect of thermal stresses on the pressure vessel wall sections due to the high temperature heating fluid passing through the heat exchange sections.

A flange 50 at the lower end of the member 18 is connected to feedwater inlet member 48. The flange 50 is machined to form a tight contact surface joint with tube sheet 52 of the feedwater inlet member. Rocker clamps 54 secure the feedwater inlet member 48 and the flange 50 in tightly fitting engagement while flexible membrane 56 seals the joint between the flange 50 and the member 48 against leakage from within the vessel.

Tightly packed annular shaped stainless steel plates 58 are stacked on the upper face of the tube sheet 52 to prevent any of the heating fluid from reaching the uncooled portion of the tube sheet. Within member 18 liner plates 60, 62 and 64- form a shield for keeping the heating fluid from contacting the walls of the member 18. llnlet and outlet connections 66, 68 pass through the wall of the member 18 for circulating a fluid in the annular space between the liner plates 60, 62, 64 and the adjacent cooperating walls of the member 18.

Extending from the wall of the vessel and located above the feedwater inlet member 48 is a heating fluid outlet connection 70. A sleeve 72 extends outwardly from an extension of liner plate 60 within the outlet 70 forming an annular thermal shield or sleeve within this connection.

Extending upwardly from tube sheet 52 is a plurality of feedwa-ter inlet capillary tubes 74. These tubes are back welded to the tube sheet, that is the tube sheet 52 is machined to provide projecting stubs on its inner surface, the capillary tubes are butted against the stubs, and the tube and stub are welded together from inside of the tube. Arranged about the capillary tubes and extending upwardly from liner plates 62 is a circular shield 76 which forms a space 77 closed at its base and open at its top.

Centrally located within the vessel 12 is an escape tube assembly 78 connected at its upper end to'the head member 30 and extending vertically downward to terminate open ended in a transverse plane located a short distance above the top of the capillary tubes 74. Assembly 78 is made up of an upper tube section 80, a center tube section 82 and a lower tube section 84. These tube sections are joined together to form an integral tubular con duit with slip joints 86 and 88 to permit the removal of the individual sections. Just below slip joint 88 in the lower tube section 84 is a segmented hatch 90 biased to a normally closed position. If gases accumulate in the lower end of the vessel, and there reach a predetermined pressure, the hatch will automatically open, and they will pass upwardly through the escape tube assembly 78. After the gases have been relieved the hatch will return to its closed position as shown in FIG. 1. For a more complete description of a similar construction refer to the previously mentioned application No. 261,636.

immediately above slip joints 88, 86 openings 92 and 94 in tube sections 82 and 80, respectively, provide venting means for the heating fluid. Near the upper end of the tube assembly 78, in tube section 80, additional openings 96 provide communication between the escape tube and the space 97 in the top of the vessel above the heat exchange banks.

Coiled about the lower tube section 84 is a bank of vapor generator tubes 98. Connecting tubes 100 extend from the upper end of the capillary tubes 74 to the lower end of the vapor generator tubes 98. The capillary tubes are about one-half the inside diameter of the vapor generator tubes to assure proper distribution of the feedwater from the inlet member 48 into the multiple vapor generator tubes. The bank of vapor generator tubes 98 are helically coiled in closely spaced relationship within the annular space between the concentrically disposed escapetube assembly 78 and the liner section 32. The upper portion of the upwardly extending tube bank 98 terminates in four tube groupings which open into equally spaced outlet chambers 102. These chambers, projecting radially from the vessel wall are integrally connected to the Wall section 22 with a suitable thermal sleeve-like arrangement provided for protecting the chambers 102 from thermal shock. Within each of the outlet chambers 102 the tubes comprising the vapor generating bank are secured in a vertically positioned tube sheet 104. The tube sheet is protected from the harmful eflects of the high tempera ture heating fluid which passes over the tubes by tightly fitting stainless steel plates 106 disposed adjacent the inside face of the tube sheet.

From each of the four outlet chambers 102 the vapor flows through lines 108 into four superheater inlet chambers 110 spaced 45 apart and located Within the wall section 26 superjacent the outlet chambers 102.

Spaced superheater tubes 112, connected to tube sheets 114 and opening into the inlet chambers 110, proceed first inwardly and then downwardly adjacent the inner face of the liner section 36. Closely above the vapor outlet chambers 102, the superheater tubes 112 are bent through 180 and then coil helically upward concentric with and spaced about a vertically depending baflie 116 positioned intermediate the liner section 36 and the escape tube assembly 78. This baflie extends to a point somewhat above the inlet chamber 110 and is supported by means of a suspension bracket assembly 11-8, which is secured to the upper end of the wall section 26. At the top or outlet end of the helically coiled bank, the superheater tubes, secured in tube sheets 120, open into four superheated vapor outlet chambers 122 which are spaced 45 apart. From the outlet chambers 122 the superheated steam flows to a point of use, not illustrated.

After releasing some of its heat as useful work, the steam is returned for reheating, entering four reheater steam inlet chambers 124 located in the wall sections 28 of the vessel. Tube sheets 126 secure the inlet ends of reheater tubes 128 which extend inwardly into the vessel and pass downwardly adjacent the inner face of the baf fle 116 to the same lower level as the superheater tubes 112. As with the superheater tubes, the reheater tubes 128 similarly form a number of helically coiled rows winding upwardly, concentrically spaced about the center escape tube section 82 to a point closely spaced below the slip joint 86. Next, the reheater tubes extend upwardly terminating in a tube sheet 130 associated with reheater outlet chamber 132. There are four such chambers, and the reheated vapor leaving there is conveyed by suitable piping to a point of use, not shown.

The three helically coiled banks of tubes are dependently supported within the vessel. The tubes of the vapor generator 98 and reheater tubes 128 are supported from structural steel grids 134 and 136, respectively, while the superheater tubes are supported by the brackets 118 which also support the baffle 116. In each case hanger rods 138 extend downwardly from the structural supports and in turn carry frame members 139 which provide the actual support for the tubes.

Heating fluid is supplied for flow over the reheater and superheater surfaces by two inlet conduits 140 and two superheater inlet conduits 142 passing through the upper head of the vessel. The conduits are secured to the vessel head by thermal sleeve-like connections 144 and 146 to reduce the thermal stresses which would be induced by the high temperature heating fluid entering the vessel. First inlet conduits 140 are connected into a ring header 148 which is aligned above the bank of reheater tubes 128. Four distribution tubes 150 depend from the ring header 148 to a plane immediately above the upper end of the helically coiled reheater tubes. The lower ends of the distribution tubes 150 are fitted with short horizontal distributor header sections 152 containing a plurality of spaced openings 153 for uniformly distributing the heating fluid over the bank of reheater tubes.

The second conduits 142 are connected into a ring header 154 which is aligned above the annular bank of superheater tubes 112. Eight distributor tubes 156, see FIGS. 2 and 3, extend downwardly from the ring header 154 terminating in the same plane as the distributor tubes 150 and having similar horizontal distributor header sections 158 at their lower ends, see FIG. 5.

Within the confines of the superheater and reheater tubes, the heating fluid is maintained within limits of an upper level 160 and a lower level 162. Additionally, a heating fluid level 164 is also maintained within the escape pipe section 82 which fluid enters the pipe by way of the relief openings 92.

A rupture disk 166 is located at the juncture of the upper end of the escape tube assembly 78, and the upper closure head 30 of the vessel, as a protection for the pressure parts, in the event gas pressure within the vessel exceeds a predetermined limit.

Preferably, a liquid metal such as sodium would be used as the heating fluid in the unit 10. As indicated, separate heating fluid sources supply the reheater and superheater banks to facilitate close temperature control in each of these heat exchange sections. The heating fluid is distributed over the superheater tubes by the header section 158 and flows downwardly over the tubes in the annulus formed by the baffle 116 and the liner section 36. Concurrently, fluid also flows over the reheater tubes from the distributor header 152 passing downwardly over the tubes in the annulus formed by the baflie 116 and the center section 82 of the escape tube assembly 78. At the lower end of the baflie 116, the separate streams of heating fluid combine and flow, as a single stream, downwardly over the vapor generator tubes. Below the vapor generator tubes the heating fluid passes into the annular space between liner plate 60 and the shield 76 within the member 16 and then is discharged from the vessel through the fluid heating outlet 70. In addition the space 77 is filled with a stagnant body of heating fluid maintaining the capillary tubes out of contact with the heating fluid continuously flowing out of the vessel.

In this forced-flow once-through vapor generating and superheating unit, as mentioned previously, feedwater enters through the inlet member 48 passing serially upward through the capillary tubes 74, the connecting tubes 100 and then through the vapor generating tubes 98 wherein it is vaporized, from whence the fluid discharged enters the chambers 102. It then flows through lines 108, outside of the vessel, into the superheater inlet chambers 110 for passage through the tubes 112 of the superheater bank, discharging into the superheater outlet chambers 122, from whence the superheated steam flows to a point of use and subsequent return to the reheater inlet chambers 124 for reheating in the tubes 128 of the reheater bank. After reheating the steam again flows to a point of use, not illustrated.

Because of the potentially dangerous nature of chemical interaction between water and liquid metal heating fluids, such as sodium, provision is made to relieve gases which might be generated thereby. In the present construction gases generated in the vessel can be relieved by passing upwardly through the escape tube assembly 78 and into the gas space 97 above the heating fluid in the upper end of the vessel. As previously noted, gas generated in the lower end of the vessel may pass upwardly through hatch 90 to the upper end of the vessel. The pressure surge evolved by gas generation may be absorbed within the gas space 97 in the vessel or with higher attendant gas pressures by breaking the rupture disk 166.

While the annular space 42 and space 97 are continuous, the other annular spaces 38 and 40 are sealed off by integrally attaching the liner sections 32 and 34 at their upper extremities to the associated juxtaposed wall -sec tions 20 and 22 of the pressure vessel. Preferably, an inert gas, such as argon, would be utilized in these spaces. However, in the flow space between the liner plate sec- 6 tion 60, 62 and 64 and member 18 a stagnant layer of the heating fluid would be employed.

One of the principal features of the unit 10 is the manner in which it can be readily assembled or dissassembled for inspection and maintenance with a minimum of effort. By disconnecting the exterior piping to the vessel and removing the bolts connecting the flanges of wall section 28 and head 30, the head, the attached heating fluid distribution piping system and the upper section of tube assembly 78 may be removed as a unit. The arrangement of elements in FIG. 3 clearly shows how the entire assembly may be removed through the structural steel grid 136 without encountering interference with the other vessel internals. With the head removed, access may be had to the tops of the reheater and superheater tube banks and to their structural steel supports without removing any other portions of the vessel.

After breaking the connections between the reheater inlet and outlet chambers 124, 132 and the point of use and disconnecting the lower flange of the wall section 28 from the upper flange of the wall section 26, the bank of reheater tubes 128 may be removed as a unit from the vessel. Since the reheater tube support grid 136 is attached to wall section 28, and the reheater inlet chambers 124 and 132 and outlet, respectively, are also connected to it, the reheater assembly may be removed from within the vessel without interfering with any of the other vessel internals.

Next, after breaking line 108, the wall section 26 can be separated from the wall section 24 and removed from the remainder of the vessel taking with it the bank of superheater tubes 112, the tube support structure 118 and the baflle 116 which provides the partition between the superheater and reheater tubes. All that remains within the vessel at this stage in the disassembly is the center and lower tube section-s 82 and 84 and the bank of vapor generator tubes 98.

In order to remove the bank of vapor generator tubes it is first necessary to disconnect the wall section 24 from wall section 22 and lift it from the vessel. The liner section 36 will also be removed with the wall section 24. Next the center tube 82 may be removed from the lower tube 84, the break coming at the slip joint 88. In order to remove the bank of vapor generator tubes 98, the wall section 22 must be disconnected from wall section 20 and the rocker clamps 54 disconnected from the tube sheet 52 so that the tube sheet and the capillary tubes 74 may be slid upwardly through the member 18. With the wall section 22 the bank of vapor generator tubes 98, the connecting tubes 100, the capillary tubes 74 and the tube sheet 52 with the liner plate 62 and the shield 76 will be removed as a unit. In addition, the lower tube section 84 also will be removed with the vapor generator tubes since it is carried by the structural steel support 134 which supports the vapor generator tubes. With the tubes re moved from the vessel, all that. remains is wall section 20, throat forging 16 and the integrally connected liner section 32, plus the member 18 from which the inlet member 48 and tube sheet 52 have been disconnected.

As compared with the unit disclosed in the earlier mentioned patent application No. 261,638, this unit is particularly advantageous since it provides a vapor generator tube bank which is drainable and a combined reheater, superheater arrangement which permits disposing the optimum quantity of tube surface within the minimum diameter and height of vessel. Further, by providing separate, controllable admission of heating fluid flow to the superheater and reheater tubes, control of the degree of superheating and reheating may be readily achieved.

Because of the inherently dangerous nature of interactions between water and certain heating fluids, the construction of the liner shell provides for maximum safety with a minimum of possible damage. The top of the liner section 36 is arranged so that it is always above the upper level of the heating fluid and, therefore, the heating fluid does not contact the pressure vessel walls. If there is any upsurge of heating fluid, rather than overflowing the top of the liner section, it will pass inwardly from. the openlugs 94 into the upper tube section 80.

Specifically, this unit is directed to the use of liquid sodium as the heating fluid, however, it is also readily adaptable to other types of heating fluids which may re quire protecting the vessel from the high temperature heating fluid, even though the other fluids may not be as likely to cause as violent reaction due to the interaction of the heating and heated fluids.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. A vapor generating superheating and reheating unit wherein a heating fluid passes in indirect heat transfer relationship with a vaporizable fluid comprising:

A. a vertically arranged pressure vessel comprising at least three separately removable circumferentially extending wall sections and a removable closure head forming the upper portion of the vessel,

B. a bank of vertically extending vapor generator tubes positioned within the lower end of the pressure vessel,

C. a vertically extending bank of superheater tubes disposed within said vessel above said bank of vapor generating tubes,

D. a vertically extending bank of reheater tubes disposed within said vessel coextensive with said bank of superheater tubes,

E. vertically extending baffle means located within said vessel between said banks of superheater and reheater tubes for forming separate heating fluid flow paths over said banks of tubes,

F. inlet means for said bank of vapor generator tubes detachably connected to said pressure vessel and positioned below said bank of tubes,

G. outlet means for said vapor generator tubes positioned above said bank of tubes and attached to a first one of said wall sections,

H. inlet means and outlet means connected to and located above said bank of superheater tubes and attached to a second one of said wall sections,

I. inlet means and outlet means connected to and located above reheater tubes and attached to a third one of said wall sections, and

J. heating fluid inlet means arranged to supply a separate stream of heating fluid to each of said banks of superheater and reheater tubes.

2. A vapor generating superheating and reheating unit as set forth in claim 1 wherein connecting tubes having a smaller inside diameter than said vapor generator tubes extend between the inlet means for said vapor generator tubes to the lower ends of said vapor generator tubes.

3. A vapor generating superheating and reheating unit as set forth in claim 2 wherein a sleeve encircles said connecting tubes extending upwardly from the inlet means for said vapor generator tubes forming a chamber about said connecting tubes.

4. A vapor generating superheating and reheating unit as set forth in claim 1 wherein a plurality of open ended vertically positioned circular liner sections are disposed closely inward from said pressure vessel and form in combination therewith annular spaces therebetween, the top of said liner sections spaced below the upper end of said pressure vessel.

. S. A vapor generating superheating and reheating unit as set forth in claim 4 wherein said wall sections are circular serially arranged and mechanically connected together to facilitate assembly and disassembly.

6. A vapor gene-rating superheating and reheating unit as set forth in claim 5 wherein said bank of superheater tubes is disposed concentrically about said bank of reheater tubes and both of said banks are vertically aligned above said bank of vapor generator tubes.

7. A vapor generating superheating and reheating unit as set forth in claim 6 wherein the wall section to which the bank of superheater tubes is attached is located between the wall sections to which bank the vapor generator and reheater tubes are attached. a

8. A vapor generating superheating and reheating unit as set forth in claim 7 wherein a first distributor assembly comprising a plurality of uniformly circumferentially spaced vertical tubeseach having a distributor header section at its lower end for supplying heating fluid to said bank of reheater tubes and a second distributor assembly comprising a plurality of uniformly circumferentially spaced vertical tubes each having a distribution header section at its lower end for supplying heating fluid to said bank of superheater tubes.

9. A vapor generating superheating and reheating unit as set forth in claim 8 wherein a heating fluid outlet is located at the lower end of said pressure vessel below said bank of vapor generating tubes.

10. A vapor generating superheating and reheating unit as set forth in claim 9 wherein an axially extending conduit is positioned within said pressure vessel passing through said banks of vapor generator and Ieheater tubes from the closure head of said vessel downwardly to at least the lower end of said vapor generator tubes for relieving gas generated within said vessel.

11. A vapor generating superheating and reheating unit as set forth in claim 10 wherein said conduit has openings therein along its length and contains a hatch near its lower end biased to a normally closed position for preventing any by-pass flow of heating fluid downwardly through the conduit and opening at a selected pressure for relieving gases generated in the lower end of said vessel.

12. A vapor generating superheating and reheating unit as set forth in claim 11 wherein each of said banks of tubes are helically coiled around said conduit substantially filling the spaces in which they are located.

13. A vapor generating superheating and reheating unit as set forth in claim 12 wherein a vertically extending cylindrically shaped bafile is arranged laterally extensive wilgh and between said banks of superheater and reheater tu es.

14. A vapor generating superheating and reheating unit as set forth in claim 13 wherein the upper end of said baflle is disposed above the distribution header sections of said first and second distribution assemblies.

15. A vapor generating superheating and reheating unit as set forth in claim 14 wherein support means provide individual pendant support for each of said banks of tubes.

16. A vapor generating superheating and reheating unit as set forth in claim 14 wherein thermal barrier means are disposed between the heating fluid and the portion of the pressure vessel to which the outlet ends of the vapor generator tubes are attached.

17. A vapor generating superheating and reheating unit wherein a heating fluid passes in indirect heat transfer relationship with a vaporizable fluid comprising:

A. a vertically arranged cylindrically shaped pressure vessel comprising at least three serially arranged mechanically connected separately removable circular wall sections and a removable head member forming the upper portion of the vessel,-

B. a number of upwardly positioned serially arranged cylindrically shaped open ended liner sections disposed inwardly from said pressure vessel and forming annular spaces therewith, the top of said liner sections being spaced below the upper end of said vessel,

C. a vertically extending bank of helically coiled vapor generator tubes positioned within said liner sections first ring header located in the upper end of said pressure vessel and aligned above said bank of reheater tubes, a second ring header located in the upper end of said pressure vessel aligned above said in the lower end of said pressure vessel, bank of superheater tubes and concentrically disposed D. a vertically extending bank of helically coiled reabout said first ring header, a plurality of downheater tubes disposed within and below the upper end Wardly extending first distribution conduits connected of said liner sections and above said bank of vapor at their upper ends to said first ring header, a first generator tubes, short horizontally extending member connected to E. a vertically extending annular shaped bank of helim the lower end of each of said first conduits for unically coiled superheater tubes disposed within said formly distributing heating fluid to said banks of reliner sections coextensive with and concentrically arheater tubes, a plurality of downwardly extending ranged about said reheater tube second distribution conduits connected at their upper F. a vertically extending cylindrically shaped bafile loends to said second ring header, a second short horicated within said liner sections and disposed between ZOIItaHY extending member Connected to th l w said banks of superheater and reheater tubes for end of each of said second conduits for uniformly forming e arate heating fluid flow th ov r id distributing heating fluid to said bank of superheater banks of tubes, tubes, G. an inlet chamber for said vapor generator tubes P mouhted tube hanger suP130rts for each of Said positioned below the bank of said tubes and detach- 20 banks of tubes, ably connected to aid pressure l, a plurality M. a vertically arranged pipe centrally located within of capillary tubes Within said vessel interconnecting Said Pressure Vfissel and Passing through Said hanks said inlet chamber and vapor generator tubes, said Of tubes, Said pip Connected a its upper nd to th capillary tubes having a smaller interior diameter head Inembfif of said Pressure Vessel and having its than the vapor generator tubes to which they are lower end p and Positioned at the lower and 0f connected for uniform distribution of feedwater to the bank of Vapor ghheratof tubes, a normally Closed id vapor generator t b hatch in said pipe arranged to open and permit high H. an outlet chamber disposed above and in communi- Pressure gases to escape from the IOWer end of the cation with said vapor generator tubes and connected Pressure Vessel, to and extending outwardly from a lower one of id N. inlet and outlet connections in said pressure vessel pressure vessel wall sections located above said tubes, Communicating with the annular Spaces formed I. a separate inlet chamber and outlet chamber in comtween the Pressure Vessel Wall Sections a liner munication with said superheater tubes connected to lions for pp y fluid t0 and for draining theSB and extending outwardly from one of said pressure p and vessel wall sections disposed above said wall section Walls forming a heating fiuit Outlet located at the incorporating the vapor generating tubes outlet chamlower and 0f the Vessel, and Plate means Spaced ber and located above the said bank of superheater Wafdly from Said Walls forming an annular flow Space tubes, therebetween. J. a separate inlet chamber and outlet chamber in communication with said reheater tubes and connected References Clted by the Exammer to and extending outwardly from one of said pressure UNITED STATES PATENTS vessel wall sections and disposed above said wall 1 33 05 10/1932 Davy 122 483 X section incorporating the superheater tubes inlet and 1 390 429 12 1932 Griswold 122 4g3 X outlet chambers, 3,126,949 3/1964 Boni et al 122 32 X K. separate heating fluid inlet means for each of said banks of superheater and reheater tubes comprising a KENNETH W. SPRAGUE, Primary Examiner. 

1. A VAPOR GENERATING SUPERHEATING AND REHEATING UNIT WHEREIN A HEATING FLUID PASSES IN INDIRECT HEAT TRANSFER RELATIONSHIP WITH A VAPORIZABLE FLUID COMPRISING: A. A VERTICALLY ARRANGED PRESSURE VESSEL COMPRISING AT LEAST THREE SEPARATELY REMOVABLY CIRCUMFERENTIALLY EXTENDING WALL SECTIONS AND A REMOVABLE CLOSURE HEAD FORMING THE UPPER PORTION OF THE VESSEL, B. A BANK OF VERTICALLY EXTENDING VAPOR GENERATOR TUBES POSITIONED WITHIN THE LOWER END OF THE PRESSURE VESSEL, C. A VERTICALLY EXTENDING BANK OF SUPERHEATER TUBES DISPOSED WITHIN SAID VESSEL ABOVE SAID BANK OF VAPOR GENERATING TUBES, D. A VERTICALLY EXTENDING BANK OF REHEATER TUBES DISPOSED WITHIN SAID VESSEL COEXTENSIVE WITH SAID BANK OF SUPERHEATER TUBES, E. VERTICALLY EXTENDING BAFFLE MEANS LOCATED WITHIN SAID VESSEL BETWEEN SAID BANKS OF SUPERHEATER AND REHEATER TUBES FOR FORMING SEPARATE HEATING FLUID FLOW PATHS OVER SAID BANKS OF TUBES, F. INLET MEANS FOR SAID BANK OF VAPOR GENERATOR TUBES DETACHABLY CONNECTED TO SAID PRESSURE VESSEL AND POSITIONED BELOW SAID BANK OF TUBES, G. OUTLET MEANS FOR SAID VAPOR GENERATOR TUBES POSITIONED ABOVE SAID BANK OF TUBES AND ATTACHED TO A FIRST ONE OF SAID WALL SECTIONS, H. INLET MEANS AND OUTLET MEANS CONNECTED TO AND LOCATED ABOVE SAID BANK OF SUPERHEATER TUBES AND ATTACHED TO A SECOND ONE OF SAID WALL SECTIONS, I. INLET MEANS AND OUTLET MEANS CONNECTED TO AND LOCATED ABOVE REHEATER TUBES AND ATTACHED TO A THIRD ONE OF SAID WALL SECTIONS, AND J. HEATING FLUID INLET MEANS ARRANGED TO SUPPLY A SEPARATE STREAM OF HEATING FLUID TO EACH OF SAID BANKS OF N SUPERHEATER AND REHEATER TUBES. 